1. Field of the Invention
The present invention relates to a lens barrel with a barrier device, and more particularly to a lens barrel equipped with a barrier device mounted in front of a photographic lens in an openable and closable manner to protect the photographic lens.
2. Description of the Related Art
In general, some lens barrels mounted on optical apparatuses, such as cameras, are provided with a barrier device, in which barrier blades configured to protect the front surface of an optical system (lens) are openable and closable in conjunction with an advancing and retracting operation of a lens barrel frame.
A conventional barrier device is configured such that a plurality of barrier blades are pivotally mounted on a lens barrel member, which holds a lens. The barrier blades are driven to be openable and closable by a barrier driving ring, which is rotatable around an optical axis.
In the barrier device, a barrier closing spring is mounted in a tensioned state between the barrier blade and the barrier driving ring to urge the barrier blade in a closing direction to cause the barrier blades to always contact the barrier driving ring, thus absorbing a relief movement of the barrier driving ring relative to the barrier blades.
Further, in the barrier device, a barrier opening spring is mounted in a tensioned state between the barrier driving ring and the lens barrel cover to urge the barrier driving ring, thereby driving the barrier blades in an opening direction.
The barrier device is further configured such that a rotational force of a rotating barrel is transmitted to the barrier driving ring via a connection shaft, as discussed in Japanese Patent Application Laid-Open No. 7-159856.
In the barrier device configured in the above-described manner, the rotating barrel rotates in a clockwise direction to transmit a rotational force of the rotating barrel to the barrier driving ring via the connection shaft.
The barrier driving ring, to which the rotational force has been transmitted, rotates in the clockwise direction, while charging the barrier opening spring, and the barrier blades follow the rotation of barrier driving ring by an urging force of the barrier closing spring, thus rotating in a counterclockwise direction. This rotation causes the barrier blades to shift to a state of covering the front surface of the lens.
In the barrier device, the rotation of the rotating barrel in the counterclockwise direction causes a contact portion between the rotating barrel and the connection shaft to be free. The barrier driving ring then rotates in the counterclockwise direction by an urging force of the barrier opening spring being charged, and the barrier blades follow the rotation of the barrier driving ring to be rotated in the clockwise direction. This rotation causes the barrier blades to shift to a state of opening the front surface of the lens.
The barrier blades, which are in a fully open state, contact stoppers, so that a rotation thereof in the clockwise direction is restricted. Accordingly, the rotation of the barrier driving ring is stopped.
When a rotation of the barrier blades in the closing direction is disabled by some obstacles (e.g., foreign substance such as sand) in the process of a closing operation, the barrier closing spring is charged by a rotation of the barrier driving ring in the clockwise direction, so that the rotation of the barrier driving ring in the clockwise direction is enabled. Thus, in the barrier device, the barrier closing spring acts as a member that allows a relief movement of the barrier driving ring relative to the barrier blades, which prevents mechanical breakdown from occurring.
There is a strong demand for reductions in size of cameras on which a lens barrel with a barrier device as described above is mounted. To achieve the reduction in size of the lens barrel with a barrier device, it is effective to decrease a diameter of the lens barrel equipped with a barrier device by decreasing a retraction space of the barrier blades for retraction with a good efficiency.
Thus, conventionally, in a lens barrel equipped with a barrier device for opening and closing a photographing opening portion formed in substantially rectangular shape, a method for decreasing a diameter of the lens barrel is discussed (see Japanese Patent Application Laid-Open No. 7-191380). In the method for decreasing a diameter of the conventional lens barrel, the lens barrel is configured to enhance a space efficiency of the barrier blades with respect to the size of the photographing opening portion by setting an optimum shape of the barrier blades and a retraction position thereof with respect to the photographing opening portion.
In the barrier device discussed in Japanese Patent Application Laid-Open No. 7-191380, a rotation shaft of the barrier blade is mounted on a barrier driving ring, which rotates around an optical axis, and a follower provided at a tip of the barrier blade is caused to engage with a cam groove provided on a cover member. In the barrier device configured in this manner, when the barrier driving ring is rotated, the rotation shaft of the barrier blade performs a rotational movement around the optical axis, and at the same time, the tip of the barrier blade moves along a path defined by the cam groove. Consequently, in the barrier device, the position and orientation of the barrier blades when the barrier blades are opened can be adjusted by changing the amount of rotation of the barrier driving ring and the path defined by the cam groove. Thus, a retraction space of the barrier blades when the barrier blades are opened can be optimized.
However, in the lens barrel with a barrier device, when a configuration is employed in which barrier blades are pivotally mounted on a lens barrel member, a retraction space when the barrier blades are opened is fixedly determined. Accordingly, in this case, there is no room for designing the lens barrel to be reduced in size by decreasing a retraction space when the barrier blades are opened. Thus, it is difficult to attain the reduction in size of the lens barrel.
In addition, in the lens barrel with a barrier device, the barrier blades may fail to rotate in a closing direction due to some obstacles (e.g., foreign substance such as sand) during the closing operation. In order to deal with the problem, in the configuration where the barrier blades are pivotally mounted on the lens barrel member, dedicated parts (barrier closing spring) need to be provided in the lens barrel for absorbing a relief movement of the barrier driving ring relative to the barrier blades when the barrier blades fail to perform the closing operation. Accordingly, it is difficult to achieve a reduction in the size of the lens barrel.
Further, in the lens barrel with a barrier device that is configured such that the rotation shaft of the barrier blade rotates around the optical axis, the tip of the barrier blade is configured to slide within the cam groove during the opening and closing operation of the barrier blades. For this reason, the barrier blades cannot move in a closing direction during the closing operation if there are obstacles (e.g., foreign substance such as sand) between the tip of the barrier blade and the cam groove. When a movement of the barrier blades is blocked, the barrier driving ring is also blocked from rotating in the closing direction. For this reason, the barrier driving ring may become unable to rotate in the closing direction, so that the lens barrel may not be retracted.